Comparative Investigation of Clotting and Chromogenic Assays for Heparin and Low Molecular Weight Heparin-(Oid) in Plasma of Volunteers and Patients

Abstract

Two recently developed and simplified anti-Xa methods, a chromogenic assay and a clot-based assay (Heptest) were investigated on their accuracy and ex-vivo characteristics. The coefficients of variation (c.v.) for heparin, a heparin fragment (K 2165) and a LMW hepa-rinoid (Org 10172) were respectively: Heptest, within assay c.v.: 5.4; 4.5; 5.0 % between-assay c.v.: 7.8; 5.8; 9.5 %. Chromogenic Anti-Xa assay, within assay c.v.: 3.7; 5.6; 4.6 %, between assay c.v.: 6.6; 8.2; 12.1 %. In plasma samples obtained from volunteers and patients who participated in clinical studies using heparin, K 2165 and Org 10172, the ex-vivo correlation between both assays were determined. Generally, heparin and K 2165 induced anti-Xa activities correlated very well (0.83 < r< 0.99) and the slopes of the regression lines approached the value of 1. K 2165 in haemodial-ysis patients produced much higher Heptest values compared to the chromogenic anti-Xa assay, for which no explanation is provided. For Org 10172 the anti-Xa assay was more sensitive than the Heptest, although both tests detected anti-Xa activities at very low levels (± 0.02 U/ml). After s.c. injection of Org 10172 a poor correlation was found (r=0.49), which may be due to inter-individual differences in bio-availability. In conclusion, the chromogenic anti-Xa assay and the Heptest are accurate and sensitive assays. However, the tests give substantial differences in results depending upon the heparin preparation and patient category treated.